1. Field of the Invention
This invention relates to an organic coating film capable of effectively absorbing laser beams, especially longer wavelength beams emitted from semiconductor lasers, and capable of converting these beams into other energy. More particularly, this invention relates to a novel organic coating film adaptable as an electrophotographic photosensitive coat for electrophotographic printers employing a semiconductor laser as light source, as a coat for optical disks where the writing and reproduction of information are possible with semiconductor laser beams, as an infrared cutting filter, etc.
2. Description of the Prior Art
The electrophotographic printer employing a semiconductor laser as light source can form reproduced images by modulating the laser with electric signals in response to the given information image, scanning a photosensitive member with the modulated laser beam to form an electrostatic latent image, developing the latent image with a toner, and transferring the toner image. Lasers generally used for this purpose are gas lasers such as a helium-cadmium laser (wavelength: 441.6 nm), a helium-neon laser (wavelength: 632.8 nm), and the like. Accordingly, photosensitive members spectrally sensitized up to about 650 nm are adaptable for those light sources. Such photosensitive members hitherto known include, for example, those having a photosensitive layer comprising a charge transfer complex of polyvinylcarbazole with trinitrofluorenone, those having a photosensitive layer consisting of a vapor-deposited layer of tellurium sensitized with selenium, those having photosensitive layers: a charge transport layer of selenium vapor-deposited upon a conductive layer and a selenium-tellurium layer vapor-deposited upon the selenium layer, those having a photosensitive layer of cadmium sulfide spectrally sensitized with a sensitizing dye, and those having two photosensitive layers which function separately as a charge generation layer containing an organic pigment and a charge transport layer and are spectrally sensitized to longer wavelengths.
On the other hand, the recording film used in the optical disk technique can store information in a high density as a spiral or circular track of fine pits (e.g. about 1.mu. in diameter) optically detectable. For writing information on such disk, the laser-sensitive layer thereof is spirally or circularly scanned with a converged laser beam (modulated in response to the information), thereby forming a spiral or circular track of pits where the laser beam falls on. The laser-sensitive layer can form optically detectable pits by absorbing laser energy. For instance, in a thermal mode recording system, the laser-sensitive layer can absorb laser energy and form fine pits at the absorption points by evaporation or melting. In another thermal mode recording system, pits having optically detectable density difference can be formed with absorbed laser energy at the points irradiated with a laser beam.
The information recorded on an optical disk can be read by tracing the track of pits with a laser beam and detecting optical difference between the pit and the pit-less area. For instance, the track is traced with a laser beam and the energy reflected from the disk is monitored with a photodetector. The laser beam, when falling on the pit-less area, lowers the output of the photodetector, and when hitting the pit, is sufficiently reflected from an underlying reflecting face and hence increases the output of the photodetector.
Coating films hitherto proposed as recording media for use in these optical disks are principally inorganic such as thin metal films (e.g. a vapor-deposited aluminum film), thin bismuth film, thin tellurium oxide film, and amorphous glass films of chalcogenite group.
Meanwhile semiconductor lasers have been developed in recent years, which can be made in small sizes at low costs and additionally can be modulated directly. Most of these semiconductor lasers have wavelengths of 750 nm or longer. Consequently, the laser-sensitive coat used for recording and/or reproduction with such semiconductor laser needs to have an absorption maximum in a longer wavelength region (generally the region of 750-850 nm).
However, conventional laser-sensitive coats, particularly those comprising mainly inorganic materials, have the drawbacks of poor utilization of laser energy and low sensitivity to laser beams, because of their high laser beam reflectivities. Moreover, these laser-sensitive coats are disadvantageous in that the extension of their spectral sensitivity up to 750 nm or longer complicates the structure of the laser-sensitive coat and particularly when these coats are used for electrophotography, sensitizing dyes incorporated therein fade during repetition of the charging and exposing.
Such being the case, there have been proposed in recent years organic coating films which are highly sensitive to rays of wavelengths 750 nm or longer. For example, pyrylium dye-containing organic films disclosed in U.S. Pat. No. 4,315,983 and "Research Disclosure", 20517 (1981.5) and a squarilium-dye-containing organic film disclosed in J. Vac. Sci. Technol., 18 (1), pp 105-109 (Jan./Feb. 1981) are known to be sensitive to laser beams of wavelengths 750 nm or longer.
However, organic compounds absorbing light of the longer wavelength are generally the more unstable, so that these organic films involve problems such as the liability to decompose even with a little temperature rise; in addition these films need to fulfill various requirements on performance characteristics for electrophotographic printers or optical disks. It is the present situation that the organic coating films developed up to now are not always satisfactory practicably.